Stripping compositions and methods of stripping resists

ABSTRACT

Stripping compositions for removing resist materials from substrates comprise compositions of dimethylacetamide or dimethylformamide or a mixture thereof and a tetrahydrothiophene 1,1-dioxide compound. Either or both of polyethylene glycol and a diethylene glycol monoalkyl ether may be added to provide even more effective stripping compositions.

FIELD OF THE INVENTION

This invention relates to novel resist stripping compositions and tomethods of stripping resists employing said stripping compositions. Moreparticularly, this invention relates to a novel resist strippingcomposition comprising dimethylacetamide or dimethylformamide or amixture thereof in combination with a tetrahydrothiophene 1,1-dioxidecompound which can also include polyethylene glycol and/or a diethyleneglycol monoalkyl ether and to stripping resists with said strippingcompositions.

BACKGROUND OF THE INVENTION

Modern technology utilizes positive-type resist materials forlithographically delineating patterns onto a substrate so that thepatterns can be subsequently etched or otherwise defined into thesubstrate material. The resist material is deposited as a film and thedesired pattern is defined by exposing the resist film to energeticradiation. Thereafter the exposed regions are subject to a dissolutionby a suitable developer liquid. After the pattern has been thus definedin the substrate the resist material must be completely removed from thesubstrate to avoid adversely affecting or hindering subsequentoperations or processing steps.

It is necessary to such a photolithographic process that the photoresistmaterial, following pattern delineation, be evenly and completelyremoved from all unexposed areas so as to permit further lithographicoperations. Even the partial remains of a resist in an area to befurther patterned is undesirable. Also, undesired resist residuesbetween patterned lines can have deleterious effects on subsequentprocesses, such as metallization, or cause undesirable surface statesand charges.

Heretofore the resist materials have been removed by stripping agentscontaining one or more of the following: halogenated hydrocarbons, forexample, methylene chloride or tetrachloroethylene; amines and theirderivatives such as dimethylformamide, N-methyl-2-pyrrolidone,diethanolamine and triethanolamine; glycol ethers such as ethyleneglycol monoethyl ether, 2-butoxyethanol, 2-(2-butoxyethoxy)ethanol, andthe acetates thereof; ketones such as methyl ethyl ketone, acetone,methyl isobutyl ketone and cyclohexanone, as well as such materials asdioxane, sodium phenolate, isopropyl alcohol, sulfuric acid/nitric acidmixtures, persulfuric acid mixtures such as Caro's acid and sulfuricacid/ammonium persulfate, and mixtures of caustic and phenol derivativesas well as various other materials.

However, there are various and numerous drawbacks and disadvantages withthese various materials. Among the one or more drawbacks anddisadvantages found in the use of each such stripping agents there maybe mentioned the following: undesirable flammability, volatility, odorand toxicity; incomplete removal of all resist film; effectiveness onlyon certain resist films; attack of components other than the resistmaterial, such as attack of metal substrates by the stripping agent;safely in handling and disposal of the stripper; and the undesirednecessity for use at specified elevated temperatures when selectedresists are being stripped. Furthermore, the limited strippingcapabilities of the stripping agents is a very decided drawback.Additionally, many such strippers are not sufficiently effective againstresist materials that are subject to a severe post-baking operationthereby limiting their usefulness. In some of the strippers the presenceof water is extremely detrimental. Additionally, for those strippingapplications requiring inertness of the agent to metal substrates,toxicity during handling and difficulty of disposal are primarydrawbacks.

SUMMARY OF THE INVENTION

It has now been found that a suitable photoresist stripping compositionin which the hereinbefore mentioned disadvantages and drawbacks areeliminated or substantially reduced and in which the range of usefulnessof the stripping composition is greatly extended can be obtained inaccordance with the teachings of the present invention. The novelstripping compositions also exhibit a synergistically enhanced strippingaction and provide resist stripping capabilities not possible from theuse of the individual components used alone as photoresist strippers.The novel stripping compositions of this invention comprise a mixture offrom about 30 to about 90 percent by weight of a dimethylacetamide ordimethylformamide or a mixture thereof and from about 10 to about 70percent by weight of a tetrahydrothiophene-1,1-dioxide compound.

Even more effective stripping compositions are provided if there isadded to the basic mixture either or both of the following materials;from about 3 to about 20 percent by weight of polyethylene glycol and/orfrom about 10 to about 30 percent by weight of a diethylene glycolmonoalkyl ether. The presence of water in the stripping compositions ofthis invention is not detrimental and can be present in an amount fromabout 0 to about 10 percent by weight without undue adverse effectsresulting.

The invention also relates to the use of such stripping compositions forremoving photoresist material from a substrate surface.

DETAILED DESCRIPTION OF THE INVENTION

The stripping compositions of this invention comprise strippingcompositions containing from about 30 to about 90 weight percent,preferably from about 45 to about 90 weight percent, more preferablyfrom about 60 to about 70 weight percent, and most preferably about 70weight percent of a dimethylacetamide, dimethylformamide or a mixturethereof, and from about 10 to about 70 weight percent, preferably fromabout 10 to about 55 weight percent, more preferably about 30 to about40 weight percent, and most preferably about 30 weight percent of atetrahydrothiophene-1,1-dioxide compound of the general formula ##STR1##wherein R¹ is hydrogen, methyl or ethyl.

As examples of tetrahydrothiophene-1,1-dioxide compounds of thehereinbefore set forth formula suitable for use in the compositions ofthis invention there may be mentioned for examplestetrahydrothiophene-1,1-dioxide, methyl tetrahydrothiophene-1,1-dioxideand ethyl tetrahydrothiophene-1,1-dioxide. Especially preferred istetrahydrothiophene-1,1-dioxide.

An even more effective and desirable stripping composition is providedwhen from about 3 to about 20 weight percent, preferably about 5 toabout 15 weight percent, and most preferably about 6 weight percentpolyethylene glycol is added to the aforementioned stripping mixture.Another effective and desirable stripping composition is provided whenfrom about 10 to about 30 weight percent, preferably from about 15 toabout 20 weight percent and most preferably about 17 weight percent of adiethylene glycol monoalkyl either, preferably2-(2-ethoxyethoxy)ethanol, is added to the mixture of adimethylacetamide, or dimethylformamide and atetrahydrothiophene-1,1-dioxide compound. The diethylene glycolmonoalkyl ethers that may be employed in the compositions of thisinvention are those of the formula HOCH₂ CH₂ --O--CH₂ CH₂ --O--R²wherein R² is alkyl of 1 to 4 carbon atoms. Examples of such compoundsfor use in the compositions of this invention are for example, themonomethyl-, monoethyl- and monobutyl- ethers of diethylene glycol.Expecially preferred is 2-(2-ethoxyethoxy)ethanol.

A still more preferred stripping composition of this invention comprisesa stripping composition wherein all four of the hereinbefore mentionedmaterials are present in the composition in the weight percentspreviously stated.

A most preferred stripping composition of this invention comprises amixture of from about 51% dimethylacetamide of dimethylformamide, about26% tetrahydrothiophene-1,1-dioxide, about 17% 2-(2-ethoxyethoxy)ethanoland about 6% polyethylene glycol.

While the compositions of this invention can be free of water this isnot essential and water can be present in an amount of up to about 10percent by weight.

As exemplary stripping compositions of this invention there can bementioned the following compositions of Table I.

                  TABLE I                                                         ______________________________________                                                   Percent by Weight                                                             Composition                                                        Component    A      B     C    D   E    F   G    H                            ______________________________________                                        Dimethylacetamide                                                                          70     --    70   --  51   --  60   --                           Dimethylformamide                                                                          --     70    --   70  --   51  --   62                           Tetrahydrothiophene-                                                          1,1-dioxide  30     30    --   --  26   26  25   32                           3-methyl tetrahydro-                                                          thiophene-1,1-dioxide                                                                      --     --    30   30  --   --  --   --                           2-(2-ethoxyethoxy)                                                            ethanol      --     --    --   --  17   17  15   --                           Polyethylene glycol                                                                        --     --    --   --   6    6  --    6                           ______________________________________                                    

In the compositions of this invention any suitable polyethylene glycolmay be employed although polyethylene glycol of a molecular weight ofabout 200 is preferred.

The stripping compositions of this invention are effective in strippinga wide and varied range of positive photoresists. Most positivephotoresists consist of an ortho napthoquinone diazide sulfonic acidester or amide sensitizer or photoactive component, with novolak,resole, polyacrylamide or acrylic copolymer type binders or resins. Suchpositive photoresists are well known in the art. Such resists andsensitizers are described, for example, in U.S. Pat. Nos. 3,046,118;3,046,121; 3,106,465; 3,201,239; 3,538,137; 3,666,473; 3,934,957;3,984,582 and 4,007,047. As examples of such positive photoresistcompositions for which the stripping composition of this invention maybe used there may be mentioned Eastman Kodak Company photoresist Kodak809; J. T. Baker Chemical Company photoresist PR-20; Philip A. HuntChemical Corp. Waycoat HPR 104, HPR 106, HPR 204 and HPR 206photoresists; Shipley Company Inc. photoresist AZ-1350, AZ-1350B,AZ-1350H, AZ-1350J, AZ-1370, AZ-1450B, AZ-1450J, AZ-1470, AZ-2400 andAZ-111; Polychrome Corporation photoresists PC-129, PC-129SF and PC-138;FuJu Chemicals Industrial Co. photoresist FPR-200; and Tokyo Ohka KogyoCo. Ltd. photoresist OFPR-800.

The stripping compositions of this invention are effective in completelyremoving photoresist materials from substrates even when they have beensubjected to a post-bake treatment of about 150° C. for a period ofabout one hour.

The stripping compositions of this invention are especially advantageousfor numerous reasons among which may be mentioned the following. Thestripping compositions remove positive photoresist materials from metaland other substrates without attacking the substrate. The compositionsare essentially non-toxic and are water miscible. The presence of waterduring the stripping operation is not deleterious to the operation ofthe stripping composition. Unlike phenolic based strippers thecompositions of this invention require no special handling and areeasily disposed of in normal sewage treatment facilities. Moreover thebath life and stripping effectiveness of the compositions are for themost part independent of temperature. Use of the stripping compositionsof this invention requires only a subsequent rinse with deionized waterwhereas many prior strippers require the use of additional organicsolvents. The stripping compositions of this invention completely removedifficult-to-remove positive photoresists at about 75° C. or lesswhereas some prior art strippers require bath temperatures of about 95°to 100° C. Also, most positive photoresists are completely stripped inabout one minute or less while stripping times of 5 to 20 minutes arerecommended for many commercial stripping compositions.

It has been unexpectedly found that the stripping compositions of thisinvention effectively and completely remove positive photoresistmaterial from substrates which photoresist materials are not effectivelyand completely removed by the individual components of the compositionsof this invention.

The effectiveness and unexpected nature of the stripping action ofstripping composition of the invention is illustrated by the datapresented in the following Table II.

Wafer substrates were coated with positive photoresist materialsaccording to art recognized procedures and post-baked at about 150° C.for a period of about 45 minutes to one hour. Stripping baths weremaintained at constant temperature with water baths and the post-bakedcoated wafers were immersed into 600 ml beakers containing the constanttemperature stripping compositions with intermittent agitation for thespecified times after which the wafer is removed, rinsed in runningdeionized water and spin dried at 3000 rpm. Strippability was judged byinspection of the wafers to ascertain if any residue was present.

Compositions of this invention, denoted as compositions A through C,which correspond in composition to those so designated in Table I, arecompared to results obtained for the individual components alone forthree generally difficult to remove photoresists, namely Shipley'sAZ-1350J photoresist, Tokyo Ohka Kogyo Co. Ltd.'s OFPR-800 photoresistand Philip A. Hunt Chemical-Corp. HPR 204 photoresist.

                  TABLE II                                                        ______________________________________                                        Temperature °C., Time and % Removal                                    Stripping  HPR-204    AZ-1350J    OFPR-800                                    Composition                                                                              Photoresist                                                                              Photoresist Photoresist                                 ______________________________________                                        dimethyl-  25°, 51/4 min.,                                                                   75°, 2 min.,                                                                       75°, 4 min.,                         acetamide  100%       100%        100%                                        dimethyl-             75°, 41/2-5                                                                        75°, 13 min.,                        formamide             min., 100%  100%                                        tetrahydrothio-                                                                          25°, 7 min.,                                                                      75°, 8 min.,                                                                       75°, 6 min.,                         phene-1,1-dioxide                                                                        <50%       <50%        <20%                                        3-methyl tetra-                                                                          25°, 8 min.,                                                                      --          75°, 8 min.,                         hydrothiophene                                                                            75%                   <50%                                        1,1-dioxide                                                                   A          25°, 90 sec.,                                                                     --          --                                                     100%                                                               B          --         75°, ˜30° sec.,                                                       75°, ˜1 min.,                                        100%        100%                                        C          25%, 1 min.,                                                                             75%, 11/2 min.,                                                                           75%, 21/2 min.,                                        100%       100%        100%                                        ______________________________________                                    

The above examples are given merely by way of illustration and are notto be considered to limit the invention.

It is anticipated that the stripping compositions of this invention canbe used as stripping agents for positive photoresists by contacting theunexposed photoresist on a substrate with the stripping composition in avariety of means, such as by immersion in a stripping bath or byspraying the stripping composition over the surface of the unexposedphotoresist.

While the use of the above compositions for stripping photoresistmaterials from substrates has alone been illustrated it will beappreciated that the stripping compositions of the invention aresuitable for other uses which will be apparent to those skilled in theart, such as, for example, in the stripping of polymer residues fromreaction or curing vessels and the like, or for stripping coatings, suchas for example, paints and varnishes and the like, from surfaces.

We claim:
 1. A stripping composition comprising from about 30 to about90 weight percent of a compound selected from the group consisting ofdimethylacetamide, dimethylformamide and mixtures thereof, and fromabout 10 to about 70 weight percent of a tetrahydrothiophene-1,1-dioxidecompound of the formula ##STR2## wherein R¹ is selected from the groupconsisting of hydrogen, methyl or ethyl.
 2. A composition of claim 1comprising from about 45 to about 90 weight percent of a compoundselected from the group consisting of dimethylacetamide,dimethylformamide, and mixtures thereof and from about 10 to about 55weight percent tetrahydrothiophene-1,1-dioxide.
 3. A composition ofclaim 2 comprising about 70% dimethylacetamide and 30%tetrahydrothiophene-1,1-dioxide.
 4. A composition of claim 2 comprisingabout 70% dimethylformamide and 30% tetrahydrothiophene-1,1-dioxide. 5.A composition of claim 1 having from about 10 to about 30 weight percentof a diethylene glycol monoalkyl ether of the formula

    HOCH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.2 --O--R.sup.2

wherein R² is alkyl of 1 to 4 carbon atoms.
 6. A composition of claim 5having from about 2 to about 30 weight percent 2-(2-ethoxyethoxy)ethanol also present in the composition.
 7. A composition of claim 1having from about 3 to about 20 weight percent polyethylene glycol alsopresent in the composition.
 8. A composition of claim 6 having fromabout 3 to about 20 weight percent polyethylene glycol also present inthe composition.
 9. A composition of claim 8 comprising about 51%dimethylacetamide, about 26% tetrahydrothiophene-1,1-dioxide, about 17%2-(2-ethoxyethoxy) ethanol, and about 6% polyethylene glycol.
 10. Acomposition of claim 8 comprising about 50% dimethylformamide, about 26%tetrahydrothiophene-1,1-dioxide, about 17% 2-(2-ethoxyethoxy) ethanoland about 6% polyethylene glycol.
 11. The composition of claim 7 whereinthe polyethylene glycol is polyethylene glycol of molecular weight ofabout
 200. 12. The composition of claim 9 wherein the polyethyleneglycol is polyethylene glycol of molecular weight of about
 200. 13. Thecomposition of claim 10 wherein the polyethylene glycol is polyethyleneglycol of molecular weight of about
 200. 14. The composition of claim 11wherein the polyethylene glycol is polyethylene glycol of molecularweight of about
 200. 15. A method wherein unexposed photoresist isstripped from a substrate by contacting the unexposed photoresist with astripping composition, the improvement comprising utilizing as thestripping composition the composition of claim
 1. 16. A method whereinunexposed photoresist is stripped from a substrate by contacting theunexposed photoresist with a stripping composition, the improvementcomprising utilizing as the stripping composition the composition ofclaim
 2. 17. A method wherein unexposed photoresist is stripped from asubstrate by contacting the unexposed photoresist with a strippingcomposition, the improvement comprising utilizing as the strippingcomposition the composition of claim
 3. 18. A method wherein unexposedphotoresist is stripped from a substrate by contacting the unexposedphotoresist with a stripping composition, the improvement comprisingutilizing as the stripping composition the composition of claim
 4. 19. Amethod wherein unexposed photoresist is stripped from a substrate bycontacting the unexposed photoresist with a stripping composition, theimprovement comprising utilizing as the stripping composition thecomposition of claim
 5. 20. A method wherein unexposed photoresist isstripped from a substrate by contacting the unexposed photoresist with astripping composition, the improvement comprising utilizing as thestripping composition the composition of claim
 6. 21. A method whereinunexposed photoresist is stripped from a substrate by contacting theunexposed photoresist with a stripping composition, the improvementcomprising utilizing as the stripping composition the commposition ofclaim
 7. 22. A method wherein unexposed photoresist is stripped from asubstrate by contacting the unexposed photoresist with a strippingcomposition, the improvement comprising utilizing as the strippingcomposition the composition of claim
 8. 23. A method wherein unexposedphotoresist is stripped from a substrate by contacting the unexposedphotoresist with a stripping composition, the improvement comprisingutilizing as the stripping composition the composition of claim
 9. 24. Amethod wherein unexposed photoresist is stripped from a substrate bycontacting the unexposed photoresist with a stripping composition, theimprovement comprising utilizing as the stripping composition thecomposition of claim
 10. 25. A method wherein unexposed photoresist isstripped from a substrate by contacting the unexposed photoresist with astripping composition, the improvement comprising utilizing as thestripping composition the composition of claim
 11. 26. A method whereinunexposed photoresist is stripped from a substrate by contacting theunexposed photoresist with a stripping composition, the improvementcomprising utilizing as the stripping composition the composition ofclaim
 12. 27. A method wherein unexposed photoresist is stripped from asubstrate by contacting the unexposed photoresist with a strippingcomposition, the improvement comprising utilizing as the strippingcomposition the composition of claim
 13. 28. A method wherein unexposedphotoresist is stripped from a substrate by contacting the unexposedphotoresist with a stripping composition, the improvement comprisingutilizing as the stripping composition the composition of claim 14.